1. Field of the Invention
The present invention relates to a phosphor comprising, as a host crystal, an AlON (oxynitride aluminum) crystal, an AlON solid solution crystal, or an inorganic crystal having the same crystal structure as AlON; a manufacturing method thereof; and an application thereof. More specifically, the application relates to a lighting device and an emission apparatus of an image display device utilizing features of the phosphor, that is, property of emitting light having a peak in a wavelength range of 300 nm or longer and 700 nm and shorter.
2. Description of Related Art
The phosphor is utilized in a fluorescent display tube (VFD: vacuum-fluorescent display), a field emission display (FED: Field Emission Display) or SED (Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to make the phosphor emit the fluorescence and the phosphor is excited by an excitation source with high energy such as vacuum ultraviolet rays, ultraviolet rays, an electron beam, or blue light so as to emit visible light rays. However, as a result of the phosphor being exposed to such excitation source, the luminance of the phosphor tends to decrease. Therefore, a phosphor having little degradation in the brightness is desired. Therefore, it has been proposed not to uses an conventional phosphor such as silicate phosphor, phosphate phosphor, aluminate phosphor, or sulfide phosphor but instead to use a phosphor having an inorganic crystal as a host containing nitrogen in the crystal structure such as a sialon phosphor, an oxynitride phosphor, or a nitride phosphor as a phosphor having little degradation in brightness.
As an example of these sialon phosphors is one manufactured by the following manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), and Europium oxide (Eu2O3) are mixed in predetermined molar ratios and the resultant mixture is fired by a hot press method in one atmospheric pressure (0.1 MPa) of nitrogen atmosphere at 1700° C. for one hour (for example, refer to Patent Document 1). It was reported that α-sialon activated with Eu ion (Eu2+) manufactured by the above process became a phosphor that emitted yellow light of wavelength range of 550 nm to 600 nm if excited by blue light having a wavelength range of 450 to 500 nm. A phosphor in which a rare-earth element is added to β-type sialon is also known (refer to Patent Document 2) and it is shown that phosphors activated by Tb, Yb, and Ag are ones which emit green light of 525 nm to 545 nm. It is also known that β-type sialon activated by Eu2+ becomes a phosphor of green color (refer to Patent Document 3).
As an example of the oxynitride phosphor, a blue phosphor activated by Ce having a host crystal of JEM phase (LaAl(Si6-zAlz)N10-zOz) (refer to Patent Document 4) and a blue phosphor activated by Ce having a host crystal of La3Si8N11O4 (refer to Patent Document 5) are known.
As an example of the nitride phosphor, a red phosphor activated by Eu2+ having a host crystal of CaAlSiN3 (refer to Patent Document 6) is known. Moreover, Nonpatent Document 1 reports that as a phosphor having AlN as a host, an orange or red phosphor having an emission peak from Eu ion (Eu3+) in the range of 580 nm to 640 nm was obtained as an amorphous ceramic thin film of phosphor activated by trivalent Eu ion (Eu3+) (i.e., AlN: Eu3+) by synthesis using a magnetron sputtering method at the room temperature. In Nonpatent Document 2, it is reported that a phosphor of amorphous AlN thin film activated by Tb3+ emits green light having a peak at 543 nm upon excitation by an electron beam. In Nonpatent Document 3, a phosphor of AlN thin film activated by Gd3+ is reported. However, these kinds of phosphors based on AlN are amorphous thin films which are not suitable for any application in a light or an image display device.
As a blue phosphor for application to an image display device (VFD, FED, SED, or CRT) using an electron beam as the excitation source, a phosphor having Y2SiO5 as a host crystal and including solid-solute Ce (Patent Document 7) and a phosphor of ZnS including a solid-solute emission ion such as Ag (Patent Document 8) are reported.
The present inventors proposed a phosphor having an AlN structure crystal as a host crystal and including divalent Eu ion (Eu2+) (i.e., AlN: Eu2+) in Patent Document 9 (not yet published). The phosphor can be obtained by firing a composite of AlN to which Si3N4 and Eu2O3 are added at a higher temperature than 1800° C. and shows a blue fluorescence derived from Eu2+ as divalent Eu ions (Eu2+) are stabilized by incorporating Si, Eu, and oxygen into the AlN crystal structure.    [Patent Document 1] Specification of Japanese Patent No. 3,668,770    [Patent Document 2] Japanese Patent Application Publication No. S60-206889    [Patent Document 3] Japanese Patent Application Publication No. 2005-255895    [Patent Document 4] WO 2005/019376    [Patent Document 5] Japanese Patent Application Publication No. 2005-112922    [Patent Document 6] WO 2005/052087    [Patent Document 7] Japanese Patent Application Publication No. 2003-55657    [Patent Document 8] Japanese Patent Application Publication No. 2004-285363    [Patent Document 8] Japanese Patent Application No. 2004-234690    [Nonpatent Document 1] Meghan L. Caldwell, et al., “Visible Luminescent Activation of Amorphous AlN: Eu Thin-Film Phosphors with Oxygen”, MRS Internet Journal Nitride Semiconductor Research, Vol. 6, Num. 13, P 1-8, 2001.    [Nonpatent Document 2] H. H. Richardson, et al., “Thin-film electroluminescent devices grown on plastic substrates using an amorphous AlN: Tb3+ phosphor,” Applied Physics Letters, Vol. 80, No. 12, p. 2207-2209, 2002.    [Nonpatent Document 3] U. Vetter, et al., “Intense ultraviolet cathodoluminescence at 318 nm from Gd3+-doped AlN,” Applied Physics Letters, Vol. 83, No. 11, P 2145-2147, 2003.    [Nonpatent Document 4] H. X. Willems et. al., “Neutron diffraction of γ-aluminium oxynitride”, Journal of materials science letters, Vol. 12, p. 1470-1472, 1993.    [Nonpatent Document 5] ICSD No. 70032, ICSD (Inorganic crystal structure database) database (Fachinformationszentrum Karlsruhe, issued by Germany).